Polymer Chemistry Blog

Spotlight on Antoine Buchard: 2018 Polymer Chemistry Emerging Investigator

23 Jan 2020

This week’s issue of Polymer Chemistry is our 2020 Emerging Investigators issue, which contains articles from polymer chemistry researchers in the early stages of their independent careers and is accompanied by an Editorial from Editor-in-Chief Professor Christopher Barner-Kowollik. To celebrate this issue we are delighted to feature the profile of Dr Antoine Buchard, who published in our 2018 Emerging Investigators issue. Below, Antoine talks about his research journey and his feelings towards Polymer Chemistry!

Dr Antoine Buchard & Dr Ulrich Hintermair from The Centre for Sustainable Chemical Technologies were photogrpahed at a coffee meeting in The Edge for the University of Bath Alumni Relations Impact Report 2018. Shoot ref: 29456 Client: Rachel Skerry – Alumni Relations. Shoot Dates 8th and 9th November 2017

“I started my research career as a student working on new metal complexes for homogeneous catalysis, and only really ventured into polymer chemistry when some of our complexes showed interesting activities in the ring-opening polymerisation of lactide. Since then, I have been really interested in polymer chemistry because it is an incredibly diverse area, which I think offers a lot of creative space for both fundamental and applied work.

Today, using renewable feedstocks to make novel polymers is the underlying theme of my research program. I am particularly interested in using natural sugars as a sustainable, highly diverse and functionalisable resource to build polymers with interesting properties, including potentially less impact on the environment. Our work addresses all aspects of the development of new polymers, from the synthesis of novel monomers, the design of new polymerisation catalysts and processes (including heterogeneous (ref Polym. Chem., 2019,10, 5894-5904)), detailed mechanistic and structure-properties studies, up to the applications of the polymers themselves. Polymer Chemistry is an ideal publication platform for this research, because of the broad scope of the journal, the diversity and expertise of the editorial team, as well as the breadth of article types possible.

Our group have for example recently discovered a method that replaces phosgene with carbon dioxide for the synthesis of cyclic carbonate monomers. We have successfully applied this protocol to various sugar derivatives, including deoxyribose (ref Polym. Chem., 2018,9, 1577-1582) and thymidine (ref Polym. Chem., 2017,8, 1714-1721) and developed promising tuneable, biocompatible and biodegradable polymers, which were also tested as tissue engineering scaffolds for regenerative medicine.

We took the opportunity of the 2018 Emerging Investigator issue to explore slightly different chemistry than usual and investigate the effect of changing some oxygen atoms with sulfur in the backbones of some of our sugar-based polycarbonate (ref Polym. Chem., 2018,9, 1577-1582). To this day it is still unclear! But along the way, we developed some new methodology for use of CS2 in the cyclothio-carbonation of the trans 1,3-diol motif of ribofuranoses, and isolated the first examples of cyclic xanthate monomers derived from natural sugars. Using controlled ring-opening polymerisation, regular poly(xanthate) and alternating poly(trithio-alt-thiocarbonate) species were obtained, and we showed that the sugar backbone influenced greatly the regioselectivity of monomer opening. These polymers formed a new family of degradable sulfur-containing sustainable polymers that attracted some attention from material scientists, and that we are still investigating today and hoping to report on further soon. Featuring in the 2018 Emerging Investigator issue was a great recognition and reward for the work done in my group over the past few years, and has spurred us to keep working in this area.

I am really looking forward to the 2020 Emerging Investigator issue of Polymer Chemistry. I am always curious to discover newcomers in the field and how they envisage the field. With the biennial Pioneering Investigators issue, these issues really set themselves apart from regular issues. I have found that authors usually want to rise to the challenge and report especially exciting results, so it is often a great read!”

Read Antoine’s Polymer Chemistry papers below!

Polymer-supported metal catalysts for the heterogeneous polymerisation of lactones
Ioli C. Howard, Ceri Hammond and Antoine Buchard
Polym. Chem., 2019,10, 5894-5904

Polymers from sugars and CS₂: synthesis and ring-opening polymerisation of sulfur-containing monomers derived from 2-deoxy-D-ribose and D-xylose
Eva M. López-Vidal, Georgina L. Gregory, Gabriele Kociok-Köhn and Antoine Buchard
Polym. Chem., 2018,9, 1577-1582 (Emerging Investigator 2018 Issue)

CO₂-Driven stereochemical inversion of sugars to create thymidine-based polycarbonates by ring-opening polymerisation
Georgina L. Gregory, Elizabeth M. Hierons, Gabriele Kociok-Köhn, Ram I. Sharma and Antoine Buchard
Polym. Chem., 2017,8, 1714-1721

Polymers from sugars and CO₂: ring-opening polymerisation and copolymerisation of cyclic carbonates derived from 2-deoxy-D-ribose
Georgina L. Gregory, Gabriele Kociok-Köhn and Antoine Buchard
Polym. Chem., 2017,8, 2093-2104

Biography

Antoine is a Royal Society University Research Fellow and Reader in Chemistry within the Centre for Sustainable and Circular Technologies (CSCT) at the University of Bath (UK). His research interests include novel chemical transformations and use in catalysis of renewable resources for the synthesis of sustainable polymers and their applications. He is also a member of the UK Catalysis Hub.

Antoine studied at the École Polytechnique in France, obtaining the École Polytechnique’s Diploma and a Master’s degree in chemistry in 2006. He also completed his PhD at the Ecole Polytechnique in 2009, under the supervision of Prof Pascal Le Floch. Antoine was then a Postdoctoral Research Assistant at Imperial College with Prof Charlotte Williams. He worked Air Liquide R&D before returning to academia in 2013, as a Whorrod Research Fellow within the CSCT at the University of Bath.

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Polymer Chemistry Author of the Month: Claude St Thomas

02 Jan 2020

By Simon Harrisson.

Claude St Thomas studied chemistry at the École Normale Supérieure, Université d’État d’Haïti, Port au Prince, Haïti. In 2008, he moved to Mexico where he obtained MSc and PhD degrees in polymer chemistry at the Centro de Investigación en Química Aplicada (CIQA) under the guidance of Dr. Ramiro Guerrero Santos. During his PhD studies, he undertook two research stays at the Laboratory of Chemistry and Processes of Polymerization (LCPP), in Lyon, France under the supervision of Prof Bernadette Charleux and Dr. Franck D’Agosto. He designed a novel dual RAFT/NMP chain transfer agent for a tandem polymerization and investigated its use for preparing the self-assembled nanoparticles. This investigation was awarded with the 2015 Rafael Illescas Frisbie prize from the Mexican Chemistry Society as the best PhD thesis. In the same year, he was promoted as a CONACYT research fellow at CIQA.

His research mainly focuses on the preparation of well-defined multiblock copolymers and the development of novel associative polymers featuring stimuli-responsive groups using reversible deactivation radical polymerization (RDRP) techniques. He is also interested in the rheological properties of polymers for applications in coatings, paints, enhanced oil recovery, and water treatment.

What was your inspiration in becoming a polymer chemist?

In my childhood, I was always fascinated by nature. At the beginning, I dreamed about becoming an agronomist. However, my interest for chemistry started in high school by the teachings from chemistry lecturer Sylvain Jean Desir. There, I understood that chemistry is the basis of life. During my MSc and PhD studies I worked with materials of common and daily use and a special interest for polymer chemistry started rising.

What was the motivation behind your most recent Polymer Chemistry article?

In our research group, scientific contributions related to the preparation of water-soluble copolymers have been previously published under the supervision of Dr. Enrique Javier Jiménez Regalado using free radical polymerization. In 2014, the “Consejo Nacional de Ciencía y Tecnología” (CONACYT, México) started a new program for addressing solutions to national problems, where young researchers were engaged and assigned to specific projects. Since, I started in my current position in 2015 and inspired by the versatility of the RAFT polymerization technique, my current research work focuses on the development of novel pathways for preparing well-defined water-soluble associative copolymers.

Inspired by the RDRP techniques and their feasibility for synthesizing polymeric materials with unprecedented properties, our recent contribution describes a new strategy for preparing environmentally-friendly water-soluble associative copolymers using the RAFT technique.

Which polymer scientist are you most inspired by?

A group of scientists have impacted my career. I appreciate the discipline, rigor and professional achievements of both Prof Bernadette Charleux and Dr. Franck D’Agosto. Fascinated by RDRP techniques, I am also inspired by three experts in RDRP: Prof Craig J. Hawker, Prof. San H. Thang and Prof. Krzysztof Matyjaszewski. Their publications describing processes for synthesizing polymers with specific characteristics might allow the use of these materials in different industrial applications.

Can you name some up and coming researchers who you think will have a big impact on the field of polymer chemistry?

Based on application areas of polymeric materials, it would be difficult to mention researchers who will have a big impact on the field. Notwithstanding, I select Dr. Francesco Picchioni (University of Groningen). His research on the development of chemical materials for application in Enhanced Oil Recovery (EOR) displays great interest and could impact the field. For these researches, I am also impressed by the research works of Dr. Michael F. Cunningham (Queens University) and Sébastien Perrier (University of Warwick)

How do you spend your spare time?

Outside of professional activities, I enjoy spending time with my family (wife and four year-old daughter-Nicole) and visiting natural places. My favorite sport is soccer, so I enjoy playing it with friends. I also enjoy playing guitar and reading about new scientific developments and culture.

What profession would you choose if you weren’t a scientist?

Probably an agronomist due to my passion for natural sciences, because it was my first dream.

Read Claude’s full article now for FREE until the 31st January!

Preparation of hydrophobically modified associating multiblock copolymers via a one-pot aqueous RAFT polymerization

Claude St Thomas, Cesar Nadem Muñoz López, Enrique Javier Jiménez Regalado, Marco Antonio de Jesús Tellez, Grit Festag, Ulrich S. Schubert and Carlos Guerrero-Sánchez

We describe an efficient strategy for the preparation of hydrophobically associating multiblock copolymers using the RAFT technique. Polymerization reactions were carried out by a one-pot aqueous RAFT polymerization at 70 °C using a symmetrical trithiocarbonate as a chain transfer agent (CTA) in aqueous media. The macroRAFT polyacrylamide (PAM) was synthetized and chain extended by polymerization of N,N′-dihexylacrylamide (DHAM) and acrylamide (AM), respectively. The resultant polymers were intensely characterized by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, diffusion-ordered spectroscopy (DOSY), Fourier transform-infrared (FT-IR) spectroscopy and rheology. The structure and insertion of a hydrophobic block (PDHAM) into the backbone were carefully demonstrated. The rheological measurements confirmed the effect of the hydrophobic block number on the viscosity of polymers at different concentrations and the formation of a reversible physical network of entangled polymers in aqueous media. Moreover, the incorporation of the hydrophobic block (PDHAM) was established by the oscillatory measurement.

About the Webwriter

Simon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based at the Laboratoire de la Chimie des Polymères Organiques (LCPO) in Bordeaux. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

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Welcome to our new Associate Editor Professor Zhibo Li

10 Dec 2019

By Garima Sharma, Deputy Editor.

We are delighted to announce Professor Zhibo Li (Qingdao University of Science and Technology,) as a new Associate Editor for Polymer Chemistry!

Zhibo Li obtained his B.S. (1998) and Master (2001) degree from the University of Science and Technology of China (USTC). He then completed his Ph.D. working on self-assembly of triblock copolymers in the Chemistry Department, University of Minnesota in 2006. After that, he spent two and half years in UCLA as a postdoctoral scholar. In 2009, he became a professor in the Institute of Chemistry, Chinese Academy of Sciences, and moved to the Qingdao University of Science and Technology in 2015. He was winner of the National Science Fund for Distinguished Young Scholars (2012), and became the Fellow of Royal Society of Chemistry (2018). His research interests include design and synthesis of stimuli-responsive polypeptides, preparation of biodegradable polyesters from biobased monomers, developing organocatalysts and phosphazene superbase for ring opening (co)polymerization of cyclic esters and epoxides, and studying the self-assembly of copolymers with multi-hydrogen bonding interactions.

Read some of his recent articles below for FREE until 17th January!

Self-crosslinking assemblies with tunable nanostructures from photoresponsive polypeptoid-based block copolymers
Jirui Wei, Jing Sun, Xu Yang, Sifan Ji, Yuhan Wei and Zhibo Li
Polym. Chem., 2020, Advance Article (Part of our 2020 Emerging Investigators issue)

Fast, selective and metal-free ring-opening polymerization to synthesize polycarbonate/polyester copolymers with high incorporation of ethylene carbonate using an organocatalytic phosphazene base
Chuanzhi Wei, Xinhui Kou, Shaofeng Liu and Zhibo Li
Polym. Chem., 2019,10, 5905-5912

Phosphazene superbase catalyzed ring-opening polymerization of cyclotetrasiloxane toward copolysiloxanes with high diphenyl siloxane content
Jinfeng Shi, Na Zhao, Shuang Xia, Shaofeng Liu and Zhibo Li
Polym. Chem., 2019,10, 2126-2133

A facile method to prepare high molecular weight bio-renewable poly(γ-butyrolactone) using a strong base/urea binary synergistic catalytic system
Yong Shen, Zhichao Zhao, Yunxin Li, Shaofeng Liu, Fusheng Liu and Zhibo Li
Polym. Chem., 2019,10, 1231-1237

Schiff base and reductive amination reactions of α-amino acids: a facile route toward N-alkylated amino acids and peptoid synthesis
Xiaohui Fu, Zheng Li, Jirui Wei, Jing Sun and Zhibo Li
Polym. Chem., 2018,9, 4617-4624

Preparation of biorenewable poly(γ-butyrolactone)-b-poly(l-lactide) diblock copolyesters via one-pot sequential metal-free ring-opening polymerization
Yong Shen, Jinbo Zhang, Na Zhao, Fusheng Liu and Zhibo Li
Polym. Chem., 2018,9, 2936-2941

As a Polymer Chemistry Associate Editor, Zhibo will be handling submissions to the journal.

Why not submit your next paper to his Editorial Office?

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Welcome to our new Associate Editor Professor Rongrong Hu

06 Dec 2019

By Garima Sharma, Deputy Editor.

We are delighted to announce Professor Rongrong Hu (South China University of Technology) as a new Associate Editor for Polymer Chemistry!

Rongrong Hu received her B.S. degree from Peking University and her PhD degree from Hong Kong University of Science and Technology. She is currently a Professor of the State Key Laboratory of Luminescent Materials and Devices at South China University of Technology.

She has published over 110 peer-reviewed articles and reviews. Her research interests include (1) the development of alkyne or isocyanide-based multicomponent polymerization methodology through the combination of organic and polymer synthesis, and (2) luminescent polymers with diverse structures and applications. Her current research focuses on the development of multicomponent polymerizations of elemental sulfur and sulfur-containing functional polymers.

Read some of her recent articles below for free until the 17^th January!

Room temperature multicomponent polymerizations of alkynes, sulfonyl azides, and N-protected isatins toward oxindole-containing poly(N-acylsulfonamide)s
Liguo Xu, Fan Zhou, Min Liao, Rongrong Hu* and Ben Zhong Tang*
Polym. Chem., 2018,9, 1674-1683, Paper (Part of our 2018 Emerging Investigators series)

Red-emissive azabenzanthrone derivatives for photodynamic therapy irradiated with ultralow light power density and two-photon imaging
Qiguang Zang, Jiayi Yu, Wenbin Yu, Jun Qian, Rongrong Hu* and Ben Zhong Tang*
Chem. Sci., 2018,9, 5165-5171, Edge Article

Fluorescence visualization of crystal formation and transformation processes of organic luminogens with crystallization-induced emission characteristics
Chao Zheng, Qiguang Zang, Han Nie, Weitao Huang, Zujin Zhao, Anjun Qin, Rongrong Hu* and Ben Zhong Tang*
Mater. Chem. Front., 2018,2, 180-188, Research Article

Thermoresponsive AIE polymers with fine-tuned response temperature
Tingzhong Li, Sicong He, Jianan Qu, Hao Wu, Shuizhu Wu, Zujin Zhao, Anjun Qin, Rongrong Hu* and Ben Zhong Tang*
J. Mater. Chem. C, 2016,4, 2964-2970, Paper

As a Polymer Chemistry Associate Editor, Rongrong will be handling submissions to the journal.

Why not submit your next paper to her Editorial Office?

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Paper of the month: Synthesis of block copolymers using poly(methyl methacrylate) with unsaturated chain end through kinetic studies

02 Dec 2019

By Athina Anastasaki, Web Writer.

Chang et al. employ addition-fragmentation chain transfer to generate well-defined block copolymers.

The use of a polymethylmethacrylate (PMMA) containing an unsaturated chain end as a macroinitiator during reversible complexation mediated polymerization has been previously reported by Goto and coworkers. Typically, such macroinitiators can also be used as macromonomers to generate branched polymers via propagation. In this work, Goto and co-workers elegantly demonstrate that the occurrence of addition-fragmentation chain transfer and propagation strongly depends on the temperature during the polymerization of styrene. Through carefully monitoring the kinetics of the polymerization of styrene, the authors discovered that propagation is predominant below 60 ̊C, consistent with previous reports. However, upon elevating the temperature (e.g. 120 ̊C), addition-fragmentation chain transfer dominates instead. This discovery then allowed access to the efficient synthesis of block copolymers with PMMA and polystyrene at high temperatures. Importantly, addition-fragmentation chain transfer was also predominant over propagation during the polymerizations of acrylonitrile and acrylates yielding well-defined block copolymers. PMMAs with different molecular weights were also investigated and the polymerization was controlled utilizing iodine transfer polymerization for styrene and reversible complexation mediated polymerization for the other monomers. Such an approach is highly advantageous due to the ease of the operation and it is expected to be a practical alternative for efficient block copolymer synthesis.

Tips/comments directly from the authors:

The proper purification of polymers and the careful NMR analysis were important for obtaining the accurate kinetic data. The kinetic study provided a useful idea enabling the synthesis of block copolymers of PMMA with polystyrene (PSt).
Block copolymers of PMMA with PSt, polyacrylonitrile, and polyacrylates are accessible. Relatively high monomer conversions are achievable.
Not only the isolated alkyl iodide but also the alkyl iodide in situ generated from iodine (I₂) and azo compound can effectively be used as the initiating dormant species. The in situ method is less expensive and robust and hence can be a practically attractive

Read the full article now for FREE until 10th January!

Synthesis of block copolymers using poly(methyl methacrylate) with unsaturated chain end through kinetic studies, Polym. Chem., 2019, 10, 5617-5625, DOI: 10.1039/c9py01367a

About the web writer

Dr. Athina Anastasaki is an Editorial Board Member and a Web Writer for Polymer Chemistry. Since January 2019, she joined the Materials Department of ETH Zurich as an Assistant Professor to establish her independent research group.

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Polymer Chemistry Author of the Month: Christina Chai

15 Nov 2019

By Simon Harrisson.

Christina Chai obtained her BSc (Hons) from the University of Canterbury, Christchurch, New Zealand and her PhD in organic chemistry from the Research School of Chemistry, Australian National University, Canberra under the mentorship of the late Professor Athel Beckwith, FRS. Following her PhD, she was awarded a Samuel and Violette Glasstone Research fellowship at the University of Oxford, UK. This was followed by a Faculty position in the Department of Chemistry, Victoria University of Wellington, NZ (1991-1993) and the Department and Research School of Chemistry, Australian National University (1994-2004) where she rose to the rank of a Reader. In 2005, Christina moved to Singapore to establish a research programme on synthetic and polymer chemistry at the then newly founded Institute of Chemical and Engineering Sciences, Agency for Science Technology and Research (A*STAR). She returned to a life in academia in 2011 at the Department of Pharmacy, National University of Singapore where she has held many administrative positions. She is currently Professor and the Head of the Department of Pharmacy. Although her major research interest is on bioactive compounds, she moonlights in polymer chemistry with special interest in biomimetic materials.

What was your inspiration in becoming a scientist who works with polymers?

My PhD training was in the area of free radical chemistry with one of the free radical ‘’gods’’, the late Professor Athel Beckwith. At that time, a superb team of chemists in CSIRO Australia had developed the RAFT process which was based on the principles of radical chemistry, and I was fascinated with the numerous possibilities of this process in creating new materials. Although this fascination remained after my PhD studies, I did not have the opportunity to work with polymers until I moved to A*STAR Singapore. I continue to be intrigued with clever ways of designing functional polymers for various applications.

What was the motivation behind your most recent Polymer Chemistry article?

When I first joined NUS, I received a grant that allowed me to work on biomimetic materials, specifically mussel-inspired coatings. I was intrigued with the claims that polydopamine (PDA) is a universal coating material, and was amazed with the reported applications of polydopamine. If one read and believed all the literature, one would imagine that PDA is the answer to all our material needs. As we worked to develop PDA functional coatings, we were hampered by the lack of information on the structure of PDA. We wanted to improve the properties of PDA but how do we improve a mystery material? So we set out to understand the oxidation chemistry of dopamine, and the process of coating and of course, to attempt to elucidate the structure of PDA. I was fortunate that my PhD student at that time, Lyu Qinghua was so obsessed with this mystery that he refused to submit his thesis until he knew the answer. I am not convinced that we have completely solved the mystery (although I did manage to persuade the student to submit his thesis) but I believe that we have made significant progress in the structural elucidation. The answer is just around the corner!

Which polymer scientist are you most inspired by?

In view of my training as a free radical chemist, I was most interested in the ability to control polymer synthesis through living free radical polymerisation methods such as ATRP and RAFT. I personally know Professor San Thang, now of Monash University, who is one of the co-inventors of RAFT, and his life story and his humility despite his successes is one of my inspiration. Professor K. Matyjaszewski, the guru of ATRP and Professor Craig Hawker, with his fascinating designs of functional polymers are also heroes in my eyes.

Can you name some up and coming researchers who you think will have a big impact on the field of polymer chemistry?

Professor Molly Stevens from Imperial College London is a name that comes to mind as her research on materials for biomedical applications will be a game changer.

How do you spend your spare time?

I love reading and travelling. I read fiction and non-fiction for pleasure. My love for travel is not about visiting places of interest but to immerse myself in a different environment and culture. Although I am an introvert, I am interested in people-watching. People are fascinating subjects for study!

What profession would you choose if you weren’t a scientist?

A doctor, a nun or a scientist – This is what I would say when I was a child when people asked me what I wanted to be when I grew up. As I doubt that I would be religious enough to qualify as a nun, this just leaves being a doctor as my alternate profession that I would choose. However I love being a scientist! I constantly worry about not having enough funds to support my research. My dream is to win the lottery so that I can support my research for the rest of my career…

Is the end in sight for the structural analysis of polydopamine? What important questions remain to be answered?

Yes, I believe that the end is in sight for the structural analysis of polydopamine. I believe that fundamental studies are important if we want to advance the applications. Without knowing the structure, how do we improve the properties of the material? There are still gaps in PDA technology that needs to be addressed. For example, one would need to know how to reproducibly control the thickness and homogeneity of the material; how to reduce the coloration and improve stability…. There is so much that we do not yet know.

Read Christina’s full article now for FREE until the 21st December!

Unravelling the polydopamine mystery: is the end in sight?

Qinghua Lyu, Nathanael Hsueh and Christina L. L. Chai

Despite the prominence of polydopamine (PDA) in the field of polymer and materials chemistry since it was first reported by H. Lee, S. M. Dellatore, W. M. Miller and P. B. Messersmith, Science, 2007, 318, 426–430, the structure of PDA has been an unresolved and contentious issue. Current consensus favors polymers derived from the cyclized intermediate 5,6-dihydroxyindole (DHI). In this work, compelling evidence for the possible structure of PDA is shown via detailed mass spectroscopic studies using deuterium-labeled dopamine (DA) precursors. More specifically, the major component of PDA is shown to derive from dopaminochrome (DAC) and uncyclized DA components. One major intermediate, seen at m/z 402, is characterized as a combination of benzazepine + DAC + 2H-pyrrole, which has a chemical formula of C₂₃H₂₀N₃O₄. Furthermore, DAC forms stable complexes with DA, and is a key control point in the polymerization of PDA. The decay of DAC into DHI is a relatively slow process in the presence of excess DA, and plays a smaller role in PDA formation. This study shows the covalent connectivity in PDA from the starting DA monomer, and represents an important advance in elucidating the structure of PDA.

About the Webwriter

Simon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based in the Laboratoire des IMRCP in Toulouse. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

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Paper of the month: Ab initio RAFT emulsion polymerization mediated by small cationic RAFT agents to form polymers with low molar mass dispersity

01 Nov 2019

By Athina Anastasaki, Web Writer.

Stace et al. employ small cationic RAFT agents to produce low dispersity polymers in ab initio emulsion polymerization.

Reversible addition fragmentation chain transfer (RAFT) polymerization has revolutionized the field of polymer chemistry providing access to a wide range of materials with controlled molecular weight, functionality, end-group fidelity and dispersity. In their current contribution, the groups of Moad, Keddie and Fellows joined forces to report a range of low molar mass cationic RAFT agents that allow for predictable molecular weight and dispersity in ab initio emulsion polymerization. In particular, upon utilizing the protonated RAFT agent ((((cyanomethyl)thio)carbonothioyl)(methyl)amino)pyridin1-ium toluenesulfonate and the analogous methyl-quaternized RAFT agents, 4-((((cyanomethyl)thio) carbonothioyl)(methyl)amino)-1-methylpyridin-1-ium dodecyl sulfate, styrene could be efficiently polymerized yielding polystyrene with narrow molecular weight distributions (Đ_m 1.2–1.4). The authors attribute the success of ab initio emulsion polymerization with the former RAFT agent to the hydrophilicity of the pyridinium group which allows for the predominant partition of the water-soluble RAFT agent into the aqueous phase. The RAFT agent also gives minimal retardation. In addition, by employing 4-((((cyanomethyl)thio) carbonothioyl)(methyl)amino)-1-methylpyridin-1-ium dodecyl sulfate, a “surfactant-free” RAFT emulsion can be achieved producing a low Đ_m polystyrene although the RAFT end-group was lost upon isolating the polymer. Additional preliminary experiments were also performed demonstrating that this class of RAFT agents can be broadly applicable in ab initio emulsion polymerization of a range of other more-activated monomers including acrylates and methacrylates producing low dispersity polymers while the polymerization of less activated monomers such as vinyl acetate showed good control over the molecular weight, albeit broader molecular weight distributions. The authors are currently investigating such systems to establish their full utility in emulsion polymerization and develop robust and scalable conditions for the formation of block copolymers.

Tips/comments directly from the authors:

There are two significant challenges in implementing successful ab initio emulsion polymerization in a high throughput platform such as the Chemspeed®

Devising a protocol for vortexing/agitating so as to form, and then maintain, a stable latex. The protocol reported was the end-result of many experiments.
Degassing the reaction medium. RAFT polymerization can be successfully carried out in non-degassed media. However, for good reproducibility, optimal dispersity, high end group fidelity and acceptable polymerization rates, degassing remains important. In conducting experiments on the Chemspeed®, it is important to make sure the media to be dispensed by the robot are degassed, and that all of the solvent lines, and the solvent used to prime and wash the syringe needles are degassed.

Read the full article for FREE until 6th December!

Ab initio RAFT emulsion polymerization mediated by small cationic RAFT agents to form polymers with low molar mass dispersity, Polym. Chem., 2019, 10, 5044-5051, DOI: 10.1039/C9PY00893D

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Paper of the month: Benchtop flow-NMR for rapid online monitoring of RAFT and free radical polymerisation in batch and continuous reactors

30 Sep 2019

By Athina Anastasaki, Web Writer.

Knox et al. utilize a benchtop flow-NMR for rapid online monitoring of a range of polymerisation methodologies.

To precisely engineer macromolecular materials, close monitoring of the polymerization progress is required. Therefore, real-time online monitoring provides polymer chemists the opportunity to accurately observe and optimize their reactions. To this end, Warren and co-workers utilized benchtop flow-nuclear magnetic resonance (NMR) as a very convenient and powerful tool for real-time monitoring of polymers synthesized either by controlled radical polymerization or free radical polymerization protocols. In particular, reversible addition-fragmentation chain-transfer (RAFT) polymerization was employed to polymerize acrylamides giving very high conversions in less than 10 minutes and the kinetic profile of this reaction was efficiently captured. In a second example where RAFT dispersion polymerization was monitored. In spite of the rapid polymerization rates, high temporal resolution enabled the previse determination of the onset of rate acceleration usually observed for polymerization induced self-assembly (PISA) systems. In addition to the monitoring of the aforementioned complex systems, the free radical polymerization of methyl methacrylate was also studied. In this case, the linear semi-logarithmic plot indicated the expected pseudo-first order kinetics. The results discussed here demonstrate the power of using benchtop NMR spectrometers for online flow applications where both controlled and free radical polymerizations can be employed. It is the author’s opinion that the lower price of these instruments will improve access to NMR spectroscopy while the reduced sample preparation/time taken for analysis will increase research output.

Tips/comments directly from the authors:

Despite the reduced field strength, detailed polymerization kinetics comparable to traditional ‘high field’ NMR can be obtained since the vinyl protons are easily resolved.
Flow-NMR is a powerful tool to improve time-resolution and reduce lab workload but must be used with care – e.g. flow rate and sample cell geometry must be optimized.
Hydrogenated solvents can be used with lower-field instruments, but solvent selection is important: minimising any potential solvent overlap is key to reliable data.
Spectral corrections such as to the phase and baseline are crucial for reliable data – especially if using an automated system.

Read the full article now for FREE until 8th November!

Benchtop flow-NMR for rapid online monitoring of RAFT and free radical polymerisation in batch and continuous reactors, Polym. Chem., 2019, 10, 4774-4778, DOI: 10.1039/C9PY00982E

About the web writer

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Polymer Chemistry Author of the Month: April Kloxin

25 Sep 2019

By Simon Harrisson.

April M. Kloxin, Ph.D., is an Associate Professor in Chemical & Biomolecular Engineering and Materials Science & Engineering at the University of Delaware (UD) and a member of the Breast Cancer Research Program at the Helen F. Graham Cancer Center and Research Institute in the Christiana Care Health System. She obtained her B.S. and M.S. in Chemical Engineering from North Carolina State University and Ph.D. in Chemical Engineering from the University of Colorado, Boulder, as a NASA Graduate Student Research Program Fellow. She trained as a Howard Hughes Medical Institute postdoctoral research associate at the University of Colorado before joining the faculty at UD in 2011. Her group aims to create unique materials with multiscale property control for addressing outstanding problems in human health. Her research currently focuses on the design of responsive and hierarchically structured soft materials and development of controlled, dynamic models of disease and regeneration. Her honors include the Biomaterials Science Lectureship 2019, ACS PMSE Arthur K. Doolittle Award 2018, a Susan G. Komen Foundation Career Catalyst Research award, a NSF CAREER award, and a Pew Scholars in Biomedical Sciences award.

What was your inspiration in working with polymers?

I have always enjoyed building things and had a desire to use those skills to help people. I discovered my passion for using chemical approaches to build soft polymeric materials possessing unique and useful properties as an undergraduate and Master’s student at North Carolina State University (NCSU). At NCSU, I had the opportunity to work in a collaborative environment with many extraordinary friends and colleagues having great polymer science and engineering expertise, including my MS thesis advisors Profs. Rich Spontak and Stuart Cooper. This experience helped me understand the connection between molecular design and synthetic approaches for building polymeric materials with specific properties for a desired application. I had the opportunity to fully realize and direct this passion working at the interface between polymeric materials and biological systems under the outstanding advisement and mentorship of Prof. Kristi Anseth at the University of Colorado, Boulder, for my Ph.D. and with the many remarkable researchers in her group and at the University.

What was the motivation behind your most recent Polymer Chemistry article?

From a biological perspective, my group has a focus on understanding how changes in the structure, mechanical properties, and compositions of tissues in the human body that occur upon injury influence the function and fate of key cells in healing and disease. In this context, we have been interested in building synthetic mimics of these complex systems and processes, and we wanted to establish simple yet effective approaches for controlling the density and stiffness of soft materials when and where desired for hypothesis testing. In the Polymer Chemistry manuscript, we were inspired by the work of Prof. Matt Becker (Duke University) amongst others demonstrating how the rate of formation of water-swollen polymer networks, hydrogels, could be used to control defect formation, network heterogeneity, and thereby the mechanical properties of the resulting materials. We hypothesized that the rate-based control of properties that others observed with catalyzed step growth reactions was translatable to a photo-polymerized system, affording the implementation of a variety of photochemical controls (e.g., wavelength, intensity, time). In particular, by selecting a wavelength of light that was not centered at the maximum absorption of the photoinitiator, we were better able to control the rate of photopolymerization with an accessible bench-top visible light LED system and thereby defect formation. We then saw an opportunity to exploit dangling-end defects that were generated with this rate-based approach to increase crosslink density and ‘stiffen’ these materials with a secondary photopolymerization. We are excited about the potential that this light-triggered rate-based approach for controlling mechanical properties of polymer networks has for a number of applications, including our on-going studies of cell response to matrix stiffening.

Which polymer or materials scientists are you most inspired by?

Oh, there are so many! I am especially inspired by the work and leadership of Prof. Paula Hammond (MIT) and Prof. Kristi Anseth, who continue to blaze trials at the interface between polymers, materials, and biology to solve complex problems, and Prof. Chris Bowman (University of Colorado, Boulder) and the late Prof. Charlie Hoyle (University of Southern Mississippi), who have pioneered the use of light-triggered step growth reactions for creating polymeric materials with diverse and robust properties.

Can you name some up and coming polymer chemists who you think will have a big impact on the field?

It is an exciting time in polymer chemistry with many excellent researchers working from different perspectives to advance not only the field of polymer chemistry, but also to make fundamental breakthroughs that have an impact in biology, medicine, and energy. Selecting just a few is difficult in this context. A few that come to mind at the moment whose work I find particularly inspiring are Prof. Aaron Esser Kahn (University of Chicago) in biomolecular design of polymeric materials for rewiring the immune system, Prof. Dominik Konkolewicz (Miami University Ohio) in bioconjugations and dynamic covalent chemistries with polymeric materials, Prof. Rachel A. Letteri (University of Virginia) in peptide-polymer conjugates for multi-scale and dynamic properties, and my own new colleague Prof. Laure Kayser (University of Delaware) in conducting and semiconducting polymers.

How do you spend your spare time?

I enjoy making things, from designing materials at work to preparing satisfying meals in the kitchen at home. Breakfast foods are my favorite, and I have different recipes that I continue to hone on weekends for quick meals during the week. I also love being outside walking, hiking, or running with my friends or my husband and our two sons, particularly in the beautiful early autumn weather we currently are having.

What profession would you choose if you weren’t a chemist?

My obsession with the complexity of biological systems and improving human health would keep me in science and engineering, whether in molecular biology or bioinformatics or more applied in medicine.

Read April’s recent Polymer Chemistry article now for FREE until 31st October!

Rate-based approach for controlling the mechanical properties of ‘thiol–ene’ hydrogels formed with visible light

The mechanical properties of synthetic hydrogels traditionally have been controlled with the concentration, molecular weight, or stoichiometry of the macromolecular building blocks used for hydrogel formation. Recently, the rate of formation has been recognized as an important and effective handle for controlling the mechanical properties of these water-swollen polymer networks, owing to differences in network heterogeneity (e.g., defects) that arise based on the rate of gelation. Building upon this, in this work, we investigate a rate-based approach for controlling mechanical properties of hydrogels both initially and temporally with light. Specifically, synthetic hydrogels are formed with visible light-initiated thiol–ene ‘click’ chemistry (PEG-8-norbornene, dithiol linker, LAP photoinitiator with LED lamp centered at 455 nm), using irradiation conditions to control the rate of formation and the mechanical properties of the resulting hydrogels. Further, defects within these hydrogels were subsequently exploited for temporal modulation of mechanical properties with a secondary cure using low doses of long wavelength UV light (365 nm). The elasticity of the hydrogel, as measured with Young’s and shear moduli, was observed to increase with increasing light intensity and concentration of photoinitiator used for hydrogel formation. In situ measurements of end group conversion during hydrogel formation with magic angle spinning (MAS ¹H NMR) correlated with these mechanical properties measurements, suggesting that both dangling end groups and looping contribute to the observed mechanical properties. Dangling end groups provide reactive handles for temporal stiffening of hydrogels with a secondary UV-initiated thiol–ene polymerization, where an increase in Young’s modulus by a factor of ∼2.5× was observed. These studies demonstrate how the rate of photopolymerization can be tuned with irradiation wavelength, intensity, and time to control the properties of synthetic hydrogels, which may prove useful in a variety of applications from coatings to biomaterials for controlled cell culture and regenerative medicine.

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Paper of the month: Engineering mannosylated nanogels with membrane-disrupting properties

10 Sep 2019

By Athina Anastasaki, Web Writer.

De Coen et al. develop the engineering mannosylated nanomaterials with membrane-disruptive properties.

Engineering mannosylated nanomaterials with various functionalities can significantly contribute to the development of more effective vaccines or cancer immunotherapeutics that target immune cell subsets that express the mannose receptor. With this in mind, De Geest’s group aimed at equipping mannosylated nanogels with membrane-destabilizing properties that are responsive to the acidic pH found in intracellular vesicles, such as endosomes, but are shielded when the nanogels are intact in neutral pH. In particular, membrane destabilizing tertiary amine moieties were successfully introduced in the core of the nanogels. Subsequently and via using a pH-sensitive ketal-based crosslinker, the membrane-destabilizing properties only become activated upon pH-triggered disassembly of the nanogels into soluble unimers. In order to achieve this, the effect of tertiary amine modification of mannosylated block copolymers with N,N-dimethylamine (DMAEA) and N,N-diisopropylamine (DiPAEA) was initially evaluated. Both block copolymers showed strong haemolytic activity and the DiPAE block copolymers demonstrated an activity only at acidic endosomal pH values. To silence the membrane destabilizing activity and render the nanogels non-cytotoxic at high concentration, cross-linking of the block copolymers into nanogels was conducted. Interestingly, when a pH degradable ketal cross-linker was used, the nanogels could regain their activity by exposing them to mild acidic pH. As the authors nicely conclude, such synthetic mannosylated materials may hold promise for cytoplasmic delivery of non-membrane permeable therapeutic macromolecules.

Tips/comments directly from the authors:

Dendritic cells and macrophages reside in peripheral tissue, lymphoid organs and sites of inflammation and tumor tissue. They are a primary therapeutic target.
The use of tetraacetylated carbohydrate monomers allows for straightforward polymerization and work-up in organic media. Deacetylation is easily performed in a final step and yields hydrophilic glyconanogels.
The use of a pentafluorophenyl activated ester hydrophobic polymer bock allows for self-assembly in aprotic polar solvents. This is ideal for successive post-modification steps without facing hydrolysis as a side reaction.
Diisopropylamine motifs are highly efficient in destabilizing lipid membranes at acidic pH, presumably through hydrophobic interaction with phospholipid membranes.

Read this article for FREE until the 15th October!

Engineering mannosylated nanogels with membrane-disrupting properties Polym. Chem., 2019, 10, 4297-4307, DOI: 10.1039/C9PY00492K

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Polymer Chemistry Blog

Spotlight on Antoine Buchard: 2018 Polymer Chemistry Emerging Investigator

Polymer Chemistry Author of the Month: Claude St Thomas

Preparation of hydrophobically modified associating multiblock copolymers via a one-pot aqueous RAFT polymerization

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Welcome to our new Associate Editor Professor Rongrong Hu

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Read Christina’s full article now for FREE until the 21st December!

Paper of the month: Ab initio RAFT emulsion polymerization mediated by small cationic RAFT agents to form polymers with low molar mass dispersity

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Polymer Chemistry Author of the Month: April Kloxin

Read April’s recent Polymer Chemistry article now for FREE until 31st October!

Rate-based approach for controlling the mechanical properties of ‘thiol–ene’ hydrogels formed with visible light

Paper of the month: Engineering mannosylated nanogels with membrane-disrupting properties

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